The use of horizontal chemical vapor deposition (CVD) epitaxial reactors to deposit materials on semiconductor wafers is well known. One such horizontal reactor is comprised of a quartz tube in which a planar graphite susceptor, having a plurality of wafers thereon, is positioned. Banks of infrared (IR) lamps or radio frequency (RF) coils, mounted outside the tube are activated to heat wafers as well as the susceptor which, in turn, also heats the wafers. A flow of silicon-bearing gaseous compounds in a hydrogen ambient are then directed longitudinally into the tube. When the wafers reach a certain temperature, the silicon compounds react on the surface thereof and dissociate resulting in the desired deposited silicon layer thereon. Such a technique is effective and has been used for some time in fabricating semiconductor devices.
However, the deposition process is not selective and, at times silicon material will deposit on the inside surface of the quartz tube. When IR lamps are used the silicon deposited on the wall will absorb the radiant energy therefrom and become hotter, which leads to increased deposition thereon. This positive feedback or runaway situations inhibits efficient deposition on the wafers and can cause the destruction of the tube.
If RF coils are used, the silicon material will also deposit on the inside surface of the tube wall, however, the aforementioned positive feedback situation will not occur as the RF does not couple significantly to the silicon. However, such deposition does increase the frequency of cleaning required to provide an effective CVD process.
One technique used in an attempt to solve this problem is to direct streams of cool air at the outside surface of the tube to stop the silicon deposition on the inside surface of the tube wall. Although such a technique does tend to decrease the undesired deposition, unfortunately, some deposition still occurs with the attendant problems.
Accordingly, there is a need for a technique for substantially eliminating the deposition of silicon on the inside surface of a horizontal chemical vapor deposition reactor during the operation thereof.